linux-kernel - Re: [PATCH v3 3/3] riscv: dts: starfive: add tdm node and sound card

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Message-ID: <20230510-riveter-ridden-3f056251e623@spud>
Date:   Wed, 10 May 2023 21:22:43 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Walker Chen <walker.chen@...rfivetech.com>
Cc:     Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 3/3] riscv: dts: starfive: add tdm node and sound card

On Wed, May 10, 2023 at 05:21:21PM +0800, Walker Chen wrote:
> On 2023/5/10 16:33, Emil Renner Berthing wrote:
> > On Tue, 9 May 2023 at 20:05, Conor Dooley <conor@...nel.org> wrote:
> >>
> >> On Tue, May 09, 2023 at 08:52:48PM +0800, Walker Chen wrote:
> >> > Hi Conor/Emil,
> >> >
> >> > DT overlay is used to describe combinations of VF2 and hat.
> >> > Do you have any comments on this patch ?
> >>
> >> I seem to recall that he said at the linux-riscv sync-up call that we
> >> have* that he was not in favour of overlays for hats like this.
> >> I'll let him confirm that though, I might very well be misinterpreting or
> >> misremembering what he said.
> > 
> > What probably meant was that I didn't want a bunch of different device
> > trees for each combination board * hat. An overlay makes a lot more
> > sense. However, looking through the kernel tree there is a surprising
> > lack of overlays for hats committed already, so I suspect there is
> > some sort of policy around overlays already in place.

> About the specific usage of overlay for this board + hat, referenced to the following example in kernel:
> linux/arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-imx219.dtso
> That board is connected with imx219 sensor via mipi_csi interface. That patch was accepted in 2022.

Hmm, so spoke to Emil again today about it. In the interest of being
fair, I did go looking at that particular board & looked through their
documentation for more information on why there are overlays.
They do actually sell the bits required to use the overlays, based on
what I saw in their datasheet for the board & wiki. That said, what is
done for one arm64 platform does not necessarily apply elsewhere ;)

I'm not against allowing in-tree overlays for hats/capes/daughter-boards
that come bundled with a board, but accepting ones for a hat that
someone decided to use theoretically has no limit! The "someone" in this
case might be a StarFive developer, but it could be any random one of
your customers next!
We've got to draw a line somewhere, so my answer to the overlay *in this
case* is a no. Sorry.
When you submit your next version, please drop the overlay from this
patch.
Thanks,
Conor.

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